In hard disk drives, data is written to and read from magnetic recording media, herein called disks. Typically, one or more disks having a thin film of magnetic material coated thereon are rotatably mounted on a spindle. A read/write head mounted on an actuator arm is positioned in close proximity to the disk surface to write data to and read data from the disk surface.
During operation of the disk drive, the actuator arm moves the read/write head to the desired radial position on the surface of the rotating disk where the read/write head electromagnetically writes data to the disk and senses magnetic field signal changes to read data from the disk. Usually, the read/write head is integrally mounted in a carrier or support referred to as a slider. The slider generally serves to mechanically support the read/write head and any electrical connections between the read/write head and the disk drive. The slider is aerodynamically shaped, which allows it to fly over and maintain a uniform distance from the surface of the rotating disk.
Typically, the read/write head includes a magnetoresistive read element to read recorded data from the disk and an inductive write element to write the data to the disk. The read element includes a thin layer of a magnetoresistive sensor stripe sandwiched between two magnetic shields that may be electrically connected together but are otherwise isolated. A current is passed through the sensor stripe, and the resistance of the magnetoresistive stripe varies in response to a previously recorded magnetic pattern on the disk. In this way, a corresponding varying voltage is detected across the sensor stripe. The magnetic shields help the sensor stripe to focus on a narrow region of the magnetic medium, hence improving the spatial resolution of the read head.
The write element typically includes a coil of wire through which current is passed to create a magnetic field that can be directed toward an adjacent portion of the disk by a ferromagnetic member known as a write pole. While it is known that the write element can be arranged to either store data longitudinally or perpendicularly on the disk, most, if not all, commercial disk drives to date have utilized longitudinal recording arrangements. Although perpendicular recording techniques have the potential to allow for higher densities of recorded information, longitudinal recording is used in all current products for historical reasons. An early perpendicular recording technique is disclosed in U.S. Pat. No. RE 33,949, the contents of which are incorporated herein by reference.
The '949 patent discloses a perpendicular or vertical write head with a write pole section, downstream shield section, and a pancake coil surrounding the write pole section to generate magnetic flux therein. The shield section is disclosed to have a surface facing toward the media that is many times larger than a similarly-oriented face of the write pole. The media is disclosed to include two layers, an upper layer closer to the head having perpendicular uniaxial anisotropy and a lower layer having low magnetic reluctance (now known as the Soft Under Layer (SUL)). A high write field can then be produced between the write pole and the SUL to record information in the upper layer of the media. The write flux returns through the SUL to the downstream write shield. The return field for this design was predicted to be much lower than the write field because of the larger area of the face of the write shield as compared to the face of the write pole. It was recognized that the return field needed to be sufficiently low so as not to erase the downstream information/data under the write shield.
It has been later discovered that the predictions of a low return field in the region of the face of the write shield were not accurate under high current conditions in the electrical coils. Under these conditions, the large overall area of the electrical coils and the volume of the write shield relative to that of the write pole tended to turn the write shield into a write pole, and the design behaved like an unshielded write pole design. Since the design was unshielded and the write shield had a relatively large surface facing toward the media, the write field gradient was not as high as is desired for high density data recording. The write field gradient is the rate of change of the write field along an axis parallel to the movement of the media.
In addition, the face of the write shield in the '949 patent extended across many adjacent tracks of data. If the field into and out of this face is too large, the data stored on the adjacent tracks can be degraded as well. The phenomenon of unintentionally degrading data stored on adjacent tracks is now called adjacent track erase (ATE). The number of times that a stored bit of information can tolerate these ATE fields without degrading the stored information is a large, but finite, number. It depends on the ATE field strength relative to the threshold field for data degradation, which is known as the nucleation field.
It is desirable to design a shielded write head which does not suffer from the above drawbacks. It is against this background and a desire to improve on the prior art that the present invention has been developed.